Session Title :

Mercury contamination in rice agriculture: a growing global threat to human and wildlife health?

Synopsis :

This session will explore the biogeochemistry and biotic implications of mercury cycling in ricefields, including human exposure to mercury through rice consumption. We encourage submissions from understudied regions of rice production which examine issues of mercury speciation, export, uptake, and toxicity, as well as management opportunities to reduce mercury contamination.

Session Description :

Rice paddies are the most globally abundant wetland type in temperate and tropical latitudes. With pulsed flooding and abundant organic matter, ricefield soils are predisposed to the production of methylmercury, the form most toxic to wildlife and human health. Several recent papers have advanced our understanding of the role of rice agriculture in methylmercury production, export, and bioaccumulation. In particular, it has been shown that rice plants preferentially take up methylmercury over inorganic mercury, and that as the plant ages, methylmercury is transferred from the stalk to the seed, the part of the plant most consumed by humans and wildlife.

While fish consumption has long been known to be the primary route of human exposure to mercury in most regions of the world, more recently, rice consumption was demonstrated to be the major pathway in at least one contaminated region in China (the Wanshan Mercury Mining Area). Consumption guidelines are issued worldwide for mercury levels in fish, but there are few if any guidelines specific to mercury in rice. The World Health Organization and Food and Agriculture Organization have a provisional tolerable weekly intake for methylmercury, and the U.S. Environmental Protection Agency has a reference dose for methylmercury, but these regulations are not specific to rice. With predicted global expansion of rice crops and atmospheric mercury deposition in rice-growing regions, rice agriculture may be an underappreciated and growing threat to human and wildlife health. With scientific support, policy responses may include crop management to limit mercury bioaccumulation or human consumption guidelines for specific rice varieties.

This session will explore the biogeochemistry and ecosystem-level consequences of mercury cycling in rice agriculture and human exposure to mercury through rice consumption. Submissions providing insight into the extent of rice contamination throughout the world are encouraged, especially those that extend our knowledge of rice contamination beyond China, where the problem has been best described. We also encourage studies that add to our toolkit of analytical methods and our understanding of how and where mercury accumulates in rice plants. We encourage all presenters to consider the policy implications of their results and to speculate on appropriate management practices and regulatory approaches to the problem of mercury contamination in rice agriculture.